In chromaffin cells of adrenal the sequence of molecular events whereby the genetic code expression is regulated trans-synaptically includes an increase in the cAMP/cGMP concentration ratio, an activation of cytosol cAMP-dependent ATP-protein phosphotransferase (protein kinase) and the translocation of the low molecular weight catalytic subunit from the cytosol to the subcellular fraction. The protein kinase of nuclei is not regulated by cAMP but it increases during the trans-synaptic induction of tyrosine-3-monooxygenase (TH) as a result of a translocation of the protein kinase catalytic subunits from cytosol. Transection of the splanchnic nerve after the increase of cAMP elicited by reserpine has occurred and the cytosol protein kinase has been activated and when translocated reverts both phenomena and prevents the trans-synaptic induction of TH. Thus, the activation and translocation of protein kinase, triggered by the initial increase of cAMP, acts as a long-range messenger for the trans-synaptic regulation of the genetic code expression in adrenal medulla.